Background techniques in this technical field include Japanese Patent Application Laid-Open Publication No. 2016-085124 (Patent Document 1), Japanese Patent Application Laid-Open Publication No. 2013-242271 (Patent Document 2), US Unexamined Patent Application Publication No. 2007/0220954 (Patent Document 3), Japanese Patent Application Laid-Open Publication No. H8-271476 (Patent Document 4), and Japanese Patent Application Laid-Open Publication No. S63-128246 (Patent Document 5).
Japanese Patent Application Laid-Open Publication No. 2016-085124 (Patent Document 1) describes a gas sensor which obtains temporal change in difference between a threshold voltage of a sensor FET and a threshold voltage of a reference FET, and separates the difference of the threshold voltage caused by hydrogen gas and the difference of the threshold voltage caused by radiation from an initial value of the difference, an elapsed time of the difference, and a first-order derivative signal of the temporal change of the difference, thus measuring hydrogen gas concentration.
Japanese Patent Application Laid-Open Publication No. 2013-242271 (Patent Document 2) discloses a semiconductor gas sensor in which a gate insulation film is formed on an Si layer, a reformed TiOx film is formed on the gate insulation film, and a Pt film was formed on the reformed TiOx film. The Pt film includes a plurality of Pt crystal grains, and Ti and O are present in the crystal grain boundary gaps among the plurality of Pt crystal grains, and in particular, TiOx nanocrystals are formed around a front surface in proximity to the grain boundary triple junction.
US Unexamined Patent Application Publication No. 2007/0220954 (Patent Document 3) describes an FET gas sensor including a gas channel that diffuses a measurement gas in a gas sensing layer connected for signal reading.
Japanese Patent Application Laid-Open Publication No. H8-271476 (Patent Document 4) discloses a measurement apparatus for measuring gas components that includes a first internal space, a second internal space, first oxygen pumping means for controlling the oxygen partial pressure in the first internal space, second oxygen pumping means for pumping oxygen in the second internal space, and current detecting means for detecting a pump current flowing by operation of the second oxygen pumping means. In this measurement apparatus, a gas component amount to be measured is obtained from a value of the pump current detected by the current detecting means.
Japanese Patent Application Laid-Open Publication No. S63-128246 (Patent Document 5) describes an FET type sensor in which a film of a solid electrolyte made of a material capable of generating an electromotive force corresponding to an amount of oxygen ions at room temperature is laminated on a gate insulation film, and a metal film made of a material that catalyzes a reaction for dissociating oxygen molecules into oxygen ions is formed as a gate electrode on the film of the solid electrolyte.